The present invention relates to the making of a mixture of viscous material with solid material, and more particularly, to an apparatus and method for continuously preparing compounds in which solid fiber reinforcement or the like is impregnated in polyester resins or the like, such compounds being suitable for use in an injection molding process.
Polyester compounds reinforced with glass fibers are increasingly being used for the injection molding of composite materials. Known techniques for producing composites suitable for use in plastic molding, include a sheet molding compound (SMC), a bulk molding compound (BMC), a premix molding compound (PMC) and others. Each of these compounds has associated disadvantages. The SMC, although having relatively good strength and other desirable properties, is difficult to utilize in molds where a thick, complex shape is desired. In the BMC and PMC processes, one step in the process includes subjecting the mixture of filler and reinforcing fiber, to relatively high sheering forces and thus the reinforcement fibers are physically damaged. This limits the physical strength of the resulting compound.
An apparatus is disclosed in U.S. Pat. No. 3,932,980, in which a mixture of viscous material with solid material is continuously made. A pair of spaced mixing rolls drag the viscous filler material and the solid reinforcing material into a gap between the mixing rolls to permit the material to be mixed together. This avoids physically damaging the reinforcement fibers and in some respects represents an improvement over the above-mentioned known techniques.